Some of the x8664 constants may also be a bit off, but x8632::max-32-bit-constant-index is supposed to be an upper bound on the largest integer we can use to access an element in a 32-bit vector, i.e., a little bit less than MOST-POSITIVE-FIXNUM when misc-data-offset/misc-float-offset are accounted for. This number was much smaller on PPC, where constent displacements have to fit in 16 bits.

x862-vref is convinced that the index doesn't need a register if it's constant and we aren't bounds-checking. x862-vref1 expects its caller to have allocated a register for the index if it's a constant that's too large to be used as a memory address displacement.

I haven't checked the PPC. (Presumably, very large constant vector indices are rarely used ...)